matrix
     n 1: a rectangular array of elements (or entries) set out by rows
          and columns
     2: an enclosure within which something originates or develops
        (from the Latin for womb)
     3: the body substance in which tissue cells are embedded [syn:
        {intercellular substance}, {ground substance}]
     4: the formative tissue at the base of a nail
     5: mold used in the production of phonograph records, type, or
        other relief surface
     [also: {matrices} (pl)]
Source: WordNet® 2.0

Matrix n. [FidoNet] 1. What the Opus BBS software and sysops call
   {FidoNet}. 2. Fanciful term for a {cyberspace} expected to emerge from
   current networking experiments (see {the network}). The name of the
   rather good 1999 {cypherpunk} movie "The Matrix" played on this sense,
   which however had been established for years before. 3. The totality of
   present-day computer networks (popularized in this sense by John
   Quarterman; rare outside academic literature).


Source: The Jargon File